Stepping motors which rotate a shaft through a predetermined angle upon the application of a set of coded pulses of current to the motor coils, or windings, find use in many fields where positive, accurate, discrete movements reliably responsive to relatively high frequency pulses are desired. In a four-phase stepping motor, for example, appropriately coded combinations of four current pulses are supplied simultaneously to each of four stepping motor coils so that the stepping motor moves in sequence from one position to the next through a preselected angle. Thus, in a four-phase stepping motor the angle may be 1.8.degree. and coded pulse sequences are repetitively arranged to provide 200 discrete steps for a complete 360.degree. shaft rotation. Other embodiments may provide for different sequences of coded pulses for producing 400 discrete steps of 0.9.degree. each. The techniques for generating such pulse code sequences and for applying them to the coils of the stepping motor are well known to those in the art, the motor being capable of moving through its stepping sequence in either direction of rotation.
One of the problems in such conventional stepping motor pulse excitation circuitry lies in the need for a relatively expensive and highly regulated power supply, the high current pulses requiring the generation of relatively high power. Since such high current, high power pulses must each have a substantially constant magnitude, independently of any voltage variations in the power supply, such power supply must be highly regulated. Because of the high power requirements the cost thereof becomes more than is often justified in the particular application in which the stepping motor is to be used.
It is desirable, therefore, that the pulse excitation circuitry for a stepping motor be arranged so that the power supply for the circuit portion which supplies the high current pulses to the windings be essentially unregulated, or have low regulation, even at the high powers required.